E. coli has been shown to produce diarrhea by invading the mucosa of the small intestine and colon or by synthesizing enterotoxins. Epidemiologic studies in the past several years have demonstrated the importance of E. coli as a cause of diarrhea in adults and children. It seems to occur more often in underdeveloped countries than in developed countries, although definitive studies in the more developed countries have not been done. An E. coli (RDEC-1) isolated in my laboratory from a rabbit with diarrhea has been shown to produce diarrhea in other rabbits. RDEC-1 does not invade or produce enterotoxin but does adhere to the mucosa in very large numbers. It produces a mild, acute inflammatory response in the lamina propria and toxic changes in the epithelial cells. The objective of this study is to elucidate the mechanism by which RDEC-1 causes diarrhea. To accomplish this aim: a) concentrated supernates of broth culture of RDEC-1, b) sonicates of RDEC-1, c) cell envelopes and cell surface material of RDEC-1, and d) feces or small intestinal contents following infection with RDEC-1 will be assayed for enterotoxins, cytotoxins, and chemotaxins as described.